# EQUATION OF PARABOLA WORKSHEET

Use the information provided to write the standard form equation of each parabola.

Problem 1 :

Vertex at origin, Focus (0, 1)

Problem 2 :

Vertex at origin, Focus (2, 0)

Problem 3 :

Vertex at (1, 2), Focus (1, -1)

Problem 4 :

Vertex at (2, -1), Focus (-1, -1)

Problem 5 :

Opens up or down, Vertex at origin, Passes through (5, 75)

Problem 6 :

Opens left or right, Vertex (0,0), Passes through (-16, 2)

Problem 7 :

Opens up or down, Vertex (3, 1), Passes through (1, 9)

Problem 8 :

Opens left or right, Vertex (-1, -2), Passes through (11, 0)

Problem 9 :

Write the intercept form equation of the parabola shown below.

Use the information provided to write the standard form equation of each parabola.

Problem 10 :

Vertex (2, 3), Directrix : y = 6

Problem 11 :

Vertex (2, -2), Latus rectum : x = 1

Problem 12 :

Opens up, Vertex (-3, 4), Length of Latus rectum : 8 units

## Detailed Answer Key

Use the information provided to write the standard form equation of each parabola.

Problem 1 :

Vertex at origin, Focus (0, 1)

Solution :

Plot the vertex (0, 0) and focus (0, 1) on the xy-plane.

The parabola is open up with vertex at origin.

Standard form equation of a parabola that opens up with vertex at origin :

x2  =  4ay

Distance between the vertex and focus is 1 unit.

That is, a = 1.

x2  =  4(1)y

x2  =  4y

Problem 2 :

Vertex at origin, Focus (2, 0)

Solution :

Plot the vertex (0, 0) and focus (2, 0) on the xy-plane.

The parabola is open to the right with vertex at origin.

Standard form equation of a parabola that opens right with vertex at origin :

y2  =  4ax

Distance between the vertex and focus is 2 units.

That is, a = 2.

y2  =  4(2)x

y2  =  8x

Problem 3 :

Vertex at (1, 2), Focus (1, -1)

Solution :

Plot the vertex (1, 2) and focus (1, -1) on the xy-plane.

The parabola is open down with vertex at (1, 2).

Standard form equation of a parabola that opens down with vertex at (h, k) :

(x - k)2  =  -4a(y - h)

Vertex (h, k) = (1, 2).

(x - 1)2  =  -4a(y - 2)

Distance between the vertex and focus is 3 units.

That is, a = 3.

(x - 1)2  =  -4(3)(y - 2)

(x - 1)2  =  -12(y - 2)

Problem 4 :

Vertex at (2, -1), Focus (-1, -1)

Solution :

Plot the vertex (2, -1) and focus (-1, -1) on the xy-plane.

The parabola is open to the left with vertex at (2, -1).

Standard equation of a parabola that opens left with vertex at (h, k) :

(y - k)2  =  -4a(x - h)

Vertex (h, k) = (2, -1).

(y + 1)2  =  -4a(x - 2)

Distance between the vertex and focus is 3 units.

That is, a = 3.

(y + 1)2  =  -4(3)(x - 2)

(y + 1)2  =  -12(x - 2)

Use the information provided to write the vertex form equation of each parabola.

Problem 5 :

Opens up or down, Vertex at origin, Passes through (5, 75)

Solution :

Vertex form equation of a parabola that opens up or down with vertex at origin :

y  =  ax2

It passes through (5, 75). Substitute (x, y) = (5, 75).

75  =  a(5)2

75  =  25a

Divide each side by 25.

3  =  a

Vertex form equation of the parabola :

y  =  3x2

Problem 6 :

Opens left or right, Vertex (0,0), Passes through (-16, 2)

Solution :

Vertex form equation of a parabola that opens left or right with vertex at origin :

x  =  ay2

It passes through (-16, 2). Substitute (x, y) = (-16, 2).

-16  =  a(2)2

-16  =  a(4)

Divide each side by 4.

-4  =  a

Vertex form equation of the parabola :

x  =  -4y2

Problem 7 :

Opens up or down, Vertex (3, 1), Passes through (1, 9)

Solution :

Vertex form equation of a parabola that opens up or down with vertex at (h, k) :

y  =  a(x - h)2 + k

Vertex (h, k) = (3, 1).

y  =  a(x - 3)2 + 1

It passes through (1, 9). Substitute (x, y) = (1, 9).

9  =  a(1 - 3)2 + 1

9  =  a(-2)2 + 1

9  =  4a + 1

Subtract 1 from each side.

8  =  4a

Divide each side by 4.

2  =  a

Vertex form equation of the parabola :

y  =  2(x - 3)2 + 1

Problem 8 :

Opens left or right, Vertex (-1, -2), Passes through (11, 0)

Solution :

Vertex form equation of a parabola that opens left or right with vertex at (h, k) :

x  =  a(y - k)2 + h

Vertex (h, k) = (-1, -2).

x  =  a(y + 2)2 - 1

It passes through (11, 0). Substitute (x, y) = (11, 0).

11  =  a(0 + 2)2 - 1

11  =  a(2)2 - 1

11  =  4a - 1

Add 1 to each side.

12  =  4a

Divide each side by 4.

3  =  a

Vertex form equation of the parabola :

x  =  3(y + 2)2 - 1

Problem 9 :

Write the intercept form equation of the parabola shown below.

Solution :

Intercept form equation of the above parabola :

y  =  a(x - p)(x - q)

Because x-intercepts are (-1, 0) and (2, 0),

x  =  -1 -----> x + 1  =  0

x  =  2 -----> x - 2  =  0

Then,

y  =  a(x + 1)(x - 2)

It passes through (0, -4). Substitute (x, y) = (0, -4).

-4  =  a(0 + 1)(0 - 2)

-4  =  a(1)(-2)

-4  =  -2a

Divide each side by -2.

2  =  a

Intercept form equation of the parabola :

y  =  2(x + 1)(x - 2)

Use the information provided to write the standard form equation of each parabola.

Problem 10 :

Vertex (2, 3), Directrix : y = 6

Solution :

Plot the vertex (2, 3) and directrix y = 6 on the xy-plane.

The parabola is open down with vertex at (2, 3).

Standard equation of a parabola that opens down with vertex at (h, k) :

(x - h)2  =  -4a(y - k)

Vertex (h, k) = (2, 3).

(x - 2)2  =  -4a(y - 3)

Distance between the directrix and vertex is 3 units.

That is, a = 3.

(x - 2)2  =  -4(3)(y - 3)

(x - 2)2  =  -12(y - 3)

Problem 11 :

Vertex (2, -2), Latus rectum : x = 1

Solution :

Plot the vertex (2, -2) and latus rectum x = 1 on the xy-plane.

The parabola is open left with vertex at (2, -2).

Standard equation of a parabola that opens left with vertex at (h, k) :

(y - k)2  =  -4a(x - h)

Vertex (h, k) = (2, -2).

(y + 2)2  =  -4a(x - 2)

Distance between the latus rectum and vertex is 1 unit.

That is, a = 1.

(y + 2)2  =  -4(1)(x - 2)

(y + 2)2  =  -4(x - 2)

Problem 12 :

Opens up, Vertex (-3, 4), Length of Latus rectum : 8 units

Solution :

Standard equation of a parabola that opens up with vertex at (h, k) :

(x - h)2  =  4a(y - k)

Vertex (h, k) = (-3, 4).

(x + 3)2  =  4a(y - 4) -----(1)

Length of Latus rectum : 8.

4a  =  8

Divide each side by 4.

a  =  2

Substitute 2 for a in (1).

(x + 3)2  =  4(2)(y - 4)

(x + 3)2  =  8(y - 4)

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